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AC GENERATORS AND ALTERNATORS
The national electricity supply system of every country is an alternating current supply; in the United Kingdom and in Europe the polarity of the supply changes every V50 s or every 20 ms, and every l / 60s or 16.67 ms in the United States of America.
The basis of a simple alternator is the following one. It comprises a rotating permanent magnet (which is the rotating part or rotor) and a single-loop coil which is on the fixed part or the stator of the machine. You will see that at this instant of time, current flows into terminal A and out of terminal B (that is, terminal B is positive with respect to A so far as the external circuit is concerned).
When the magnet has rotated through 180A, S-pole the of the magnet passes across conductor A and the N-pole passes across conductor B. The net result at this time is that the induced current in the
conductors is reversed when compared with the previous case. Is That, terminal B is negative with respect to A.
In this way, alternating current is induced in each turn of wire on the stator of the alternator. In practice a single turn of wire can neither have enough voltage induced in it nor carry enough current to supply
even one electric light bulb with electricity.
A practical alternator has a stator winding with many turns of wire on it, allowing it to deal with high voltage and current. In such winding The machine is a usually distributed around the stator in many
slots in the iron circuit. The designer arranges the coil design so that the alternator generates a voltage which follows a sinewave, that is, the voltage waveform is sinusoidal.
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